Aguaclara

- Add `Component` class for sharing design inputs and serializing object properties
- Write classes for the Entrance Tank/Flocculator assembly (ETF) and all of its subcomponents
- Add tests and documentation for all new classes
- Update `Plant` class to include the ETF
- Update Python version to 3.6 due to Colab support
- Fix dependencies and add `onshape_client` for future use
- Add outer diameter functions for pipes

This release also patches a file path bug in `aguaclara.research.procoda_parser`, in which a path was incorrectly joined for Windows operating systems.

Functions in `aguaclara.research.floc_model` no longer coerce units to avoid problems with units on units. The `num_clay()` function has also been changed to `particle_number_concentration()` to extend to generic materials.

In this release,
* units are added to material properties in `aguaclara.research.floc_model`
* the "rev" (abbreviation for revolutions) unit is defined in the unit registry
* `aguaclara.research.tube_sizing` is split into two improved modules, `peristaltic_pump` and `stock_qc`
* documentation pages are added for most of the `aguaclara.research` and `aguaclara.core` modules